From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57801) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YH93T-0004xl-9D for qemu-devel@nongnu.org; Fri, 30 Jan 2015 05:44:04 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YH93R-0000I8-I4 for qemu-devel@nongnu.org; Fri, 30 Jan 2015 05:44:03 -0500 Received: from mx1.redhat.com ([209.132.183.28]:51483) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YH93R-0000I1-Aj for qemu-devel@nongnu.org; Fri, 30 Jan 2015 05:44:01 -0500 Message-ID: <54CB6060.4040603@redhat.com> Date: Fri, 30 Jan 2015 11:43:44 +0100 From: Paolo Bonzini MIME-Version: 1.0 References: <20150122085127.5276.53895.stgit@PASHA-ISP.def.inno> <20150122085254.5276.53380.stgit@PASHA-ISP.def.inno> In-Reply-To: <20150122085254.5276.53380.stgit@PASHA-ISP.def.inno> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [RFC PATCH v8 15/21] aio: replace stack of bottom halves with queue List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Pavel Dovgalyuk , qemu-devel@nongnu.org Cc: peter.maydell@linaro.org, peter.crosthwaite@xilinx.com, alex.bennee@linaro.org, mark.burton@greensocs.com, real@ispras.ru, batuzovk@ispras.ru, maria.klimushenkova@ispras.ru, afaerber@suse.de, fred.konrad@greensocs.com On 22/01/2015 09:52, Pavel Dovgalyuk wrote: > Bottom halves in AIO context are stored and removes > in LIFO order. It makes their execution non-deterministic. > This patch replaces the stack with queue to preserve the > order of bottom halves processing. > > Signed-off-by: Pavel Dovgalyuk > --- > async.c | 25 +++++++++---------------- > include/block/aio.h | 4 ++-- > include/qemu/queue.h | 7 +++++++ > 3 files changed, 18 insertions(+), 18 deletions(-) > > diff --git a/async.c b/async.c > index 2be88cc..bc6e83b 100644 > --- a/async.c > +++ b/async.c > @@ -35,7 +35,7 @@ struct QEMUBH { > AioContext *ctx; > QEMUBHFunc *cb; > void *opaque; > - QEMUBH *next; > + QSIMPLEQ_ENTRY(QEMUBH) next; > bool scheduled; > bool idle; > bool deleted; > @@ -51,10 +51,7 @@ QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque) > .opaque = opaque, > }; > qemu_mutex_lock(&ctx->bh_lock); > - bh->next = ctx->first_bh; > - /* Make sure that the members are ready before putting bh into list */ > - smp_wmb(); > - ctx->first_bh = bh; > + QSIMPLEQ_INSERT_TAIL_RCU(&ctx->bh_queue, bh, next); > qemu_mutex_unlock(&ctx->bh_lock); > return bh; > } > @@ -62,16 +59,15 @@ QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque) > /* Multiple occurrences of aio_bh_poll cannot be called concurrently */ > int aio_bh_poll(AioContext *ctx) > { > - QEMUBH *bh, **bhp, *next; > + QEMUBH *bh, *next; > int ret; > > ctx->walking_bh++; > > ret = 0; > - for (bh = ctx->first_bh; bh; bh = next) { > + QSIMPLEQ_FOREACH_SAFE(bh, &ctx->bh_queue, next, next) { > /* Make sure that fetching bh happens before accessing its members */ > smp_read_barrier_depends(); > - next = bh->next; Must use QSIMPLEQ_FOREACH. Otherwise, the access of next is before the smp_read_barrier_depends(). > if (!bh->deleted && bh->scheduled) { > bh->scheduled = 0; > /* Paired with write barrier in bh schedule to ensure reading for > @@ -90,14 +86,10 @@ int aio_bh_poll(AioContext *ctx) > /* remove deleted bhs */ > if (!ctx->walking_bh) { > qemu_mutex_lock(&ctx->bh_lock); > - bhp = &ctx->first_bh; > - while (*bhp) { > - bh = *bhp; > + QSIMPLEQ_FOREACH_SAFE(bh, &ctx->bh_queue, next, next) { > if (bh->deleted) { > - *bhp = bh->next; > + QSIMPLEQ_REMOVE(&ctx->bh_queue, bh, QEMUBH, next); > g_free(bh); > - } else { > - bhp = &bh->next; > } > } > qemu_mutex_unlock(&ctx->bh_lock); > @@ -161,7 +153,7 @@ aio_compute_timeout(AioContext *ctx) > int timeout = -1; > QEMUBH *bh; > > - for (bh = ctx->first_bh; bh; bh = bh->next) { > + QSIMPLEQ_FOREACH(bh, &ctx->bh_queue, next) { > if (!bh->deleted && bh->scheduled) { > if (bh->idle) { > /* idle bottom halves will be polled at least > @@ -204,7 +196,7 @@ aio_ctx_check(GSource *source) > AioContext *ctx = (AioContext *) source; > QEMUBH *bh; > > - for (bh = ctx->first_bh; bh; bh = bh->next) { > + QSIMPLEQ_FOREACH(bh, &ctx->bh_queue, next) { > if (!bh->deleted && bh->scheduled) { > return true; > } > @@ -311,6 +303,7 @@ AioContext *aio_context_new(Error **errp) > qemu_mutex_init(&ctx->bh_lock); > rfifolock_init(&ctx->lock, aio_rfifolock_cb, ctx); > timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx); > + QSIMPLEQ_INIT(&ctx->bh_queue); > > return ctx; > } > diff --git a/include/block/aio.h b/include/block/aio.h > index 7d1e26b..82cdf78 100644 > --- a/include/block/aio.h > +++ b/include/block/aio.h > @@ -71,8 +71,8 @@ struct AioContext { > /* lock to protect between bh's adders and deleter */ > QemuMutex bh_lock; > > - /* Anchor of the list of Bottom Halves belonging to the context */ > - struct QEMUBH *first_bh; > + /* List of Bottom Halves belonging to the context */ > + QSIMPLEQ_HEAD(, QEMUBH) bh_queue; > > /* A simple lock used to protect the first_bh list, and ensure that > * no callbacks are removed while we're walking and dispatching callbacks. > diff --git a/include/qemu/queue.h b/include/qemu/queue.h > index a98eb3a..b94c4d4 100644 > --- a/include/qemu/queue.h > +++ b/include/qemu/queue.h > @@ -268,6 +268,13 @@ struct { \ > (head)->sqh_last = &(elm)->field.sqe_next; \ > } while (/*CONSTCOND*/0) > > +#define QSIMPLEQ_INSERT_TAIL_RCU(head, elm, field) do { \ > + (elm)->field.sqe_next = NULL; \ > + *(head)->sqh_last = (elm); \ > + (head)->sqh_last = &(elm)->field.sqe_next; \ > + smp_wmb(); \ smp_wmb() must be after the (elm) assignment. Paolo > +} while (/*CONSTCOND*/0) > + > #define QSIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do { \ > if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL) \ > (head)->sqh_last = &(elm)->field.sqe_next; \ >